A canister adsorbing the volatilized gas and a solenoid valve are provided in halfway in piping feeding volatilized gas from a fuel tank into an engine. The output port of the solenoid valve is connected to the piping on the canister side, and the input port thereof is connected to an inlet pipe supplying fuel-air mixture into the engine, respectively. When the solenoid valve is opened, the negative pressure formed thereby in the inlet pipe aspirates the volatilized gas adsorbed in the canister, and the gas is fed into the engine.
The solenoid valve is opened and closed by energizing or de-energizing an electromagnetic coil. Energizing the electromagnetic coil generates an electromagnetic force, and a fixed iron core, which forms a magnetic circuit together with the electromagnetic coil, attracts a moving iron core, thereby opening the valve. In the housing of the solenoid valve are provided the input port and the output port, and in a channel connecting the input port to the output port is provided an opening and closing valve.
This opening and closing valve consists of a valve port provided in a diaphragm blocking the channel and a valve disk that can open and close the valve port. The valve disk is arranged to be driven by the moving iron core, for example, by making the valve disk itself of the moving iron core, and further, the disk is slidably engaged on the inner face of a guide cylinder standing up from the periphery of the valve port. The valve port which the valve disk freely moves toward or away from is made commonly in the form of a single round hole.
JP 2-221669 A disclosing a related technology describes that a valve opening is embodied as an annular gap coaxial to an electromagnet; the annular gap is coaxially surrounded by a ring-shaped double valve-seat on the inside and outside; and a valve element is embodied as an annular disk; thereby attaining the requisite flow cross section.
Moreover, JP 4-307186 A discloses a switching valve that is arranged such that a shutoff valve has a first closing body cooperating with a first valve seat; this first valve seat is embodied on a second closing body having a passage; the second closing body engages a second valve seat attached firmly to a casing by an action of a second spring; the preload force of this spring is greater than the valve-closing force exerted by a magnetic armature upon the first closing body in the opposite direction from this preload force; and the second closing body and the second valve seat form a pressure limiting valve disposed in the casing of the shutoff valve.
Further, JP 2000-170948 A discloses a fuel evaporative gas emission suppressing device, which is arranged such that in a solenoid valve having an input port to which pressure is supplied, an output port connected to an external device, and a plunger opening and closing a channel connecting the input port with the output port according to energizing and non-energizing a coil; a chamber is provided in the channel extending from the output port to an opening and closing part driven by the plunger.
Furthermore, JP 2003-148646 A discloses a solenoid valve including an electromagnetic coil generating electromagnetic force by energizing thereof, a stator iron core forming a magnetic circuit with the electromagnetic coil generating electromagnetic force, and a movable element; and being opened and closed by the contact and separation of the movable element to and from a valve seat; the stator iron core including an outside stator iron core formed on the outside of the electromagnetic coil and an inside stator iron core, which is formed on the inside of the electromagnetic coil, and which is located in the axial direction of the movable element; and the electromagnetic coil being covered with the outside stator iron core and at least part of the inside stator iron core.
The conventional solenoid valve is arranged as mentioned above. Consequently, in order to ensure a high flow rate, it had only to increase the opening space of the valve disk opening and closing the valve port made in the form of a single round hole. The opening space of the valve disk is roughly determined by the product of the peripheral length of the valve port multiplied into the lift of the valve disk. Therefore, first, increasing the lift of the valve disk is seemingly useful to make the opening space large. However, this results in the reduced lifetime of the valve disk and the increased operation sound.
Then, the increase of the peripheral length of the valve port is then thought to be utilized. However, when the peripheral length of the valve port is increased, the space on which pressure is exerted by the negative pressure formed at the time of valve closing increases. Accordingly, the electromagnetic attraction at the time of valve opening must be increased according to this space increase. This results in the reduced lifetime of the valve disk, the increased operation sound, and the enlarged housing.
Moreover, because the conventional solenoid valve is arranged such that the valve disk is slidably engaged on the inner face of the guide cylinder standing up from the periphery of the valve port, it has been difficult to reduce the weight of the solenoid valve.
The present invention has been made with the aim of solving the above-mentioned problems. An object of the present invention is to provide a solenoid valve by which the high flow rate can be ensured without increasing the lift of its valve disk and the electromagnetic attraction thereof, and the weight of the valve disk of which can be reduced.